Azeotropic composition containing fluorotrichloromethane and 1,1,1,3,3,3-hexafluoroisopropyl trifluoroacetate

ABSTRACT

An azeotropic composition made up of about 82.5 mol percent fluorotrichloromethane and about 17.5 mol percent 1,1,1,3,3,3-hexafluoroisopropyl trifluoroacetate, said composition boiling at about 22° C at about atmospheric pressure. This composition can be fractionally distilled from a crude mixture so as to separate the components from the mixture.

BACKGROUND OF THE INVENTION

This invention relates to a novel azeotropic composition containingfluorotrichloromethane and 1,1,1,3,3,3-hexafluoroisopropyltrifluoroacetate.

The 1,1,1,3,3,3-hexafluoroisopropyl trifluoroacetate though a novelcompound can be prepared by a number of known processes. For example,U.S. Pat. No. 3,445,507, the disclosure of which is hereby incorporatedby reference, teaches the preparation of similar esters by reaction of1,1,1,3,3,3-hexafluoroisopropanol with appropriate carboxylic acidhalides. Electrochemical fluorination to produce similar esters isbroadly disclosed in U.S. Pat. Nos. 3,511,716; 3,511,761, and 3,511,762,the disclosures of which are hereby incorporated by reference:1,1,1,3,3,3-hexafluoroisopropyl trifluoroacetate can be produced in themanner broadly described in these patents.

The products formed either by the chemical reaction or by theelectrochemical fluorination are generally in admixture with othermaterials of similar boiling points thus making separation difficult.

SUMMARY OF THE INVENTION

It is the object of this invention to provide a novel azeotropiccomposition;

IT IS A FURTHER OBJECT OF THIS INVENTION TO SEPARATE1,1,1,3,3,3-HEXAFLUOROISOPROPYL TRIFLUOROACETATE FROM CRUDE MIXTURESCONTAINING SAID ACETATE;

IT IS STILL A FURTHER OBJECT OF THIS INVENTION TO SEPARATEFLUOROTRICHLOROMETHANE FROM CRUDE MIXTURES CONTAINING SAIDFLUOROTRICHLOROMETHANE; AND

IT IS STILL A FURTHER OBJECT OF THIS INVENTION TO PRODUCE1,1,1,3,3,3-HEXAFLUOROISOPROPANOL.

In accordance with this invention, the constant boiling mixture offluorotrichloromethane and 1,1,1,3,3,3-hexafluoroisopropyltrifluoroacetate is produced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The novel azeotrope of this invention exhibits a boiling point of about22° C at about 747 torr and contains about 17.5 mol percent1,1,1,3,3,3-hexafluoroisopropyl trifluoroacetate and 82.5 mol percentfluorotrichloromethane.

This azeotrope can be used to separate 1,1,1,3,3,3-hexafluoroisopropyltrifluoroacetate from crude mixtures containing same by the addition offluorotrichloromethane or conversely to separate fluorotrichloromethanefrom crude mixtures containing same by the addition of1,1,1,3,3,3-hexafluoroisopropyl trifluoroacetate. In either event theresulting mixture is subjected to fractional distillation to recover theconstant boiling azeotrope. In the case of crude mixtures whichinherently produce a mixture of these two components, the azeotrope cansimply be distilled without the addition of any further material or asmall amount of the material present in an insufficient amount can beadded so as to remove essentially all of both components. Particularlywhere it is the main object of the operation to recover1,1,1,3,3,3-hexafluoroisopropyl trifluoroacetate, sufficientfluorotrichloromethane can be added so as to give a total of at least82.5 mol percent of the trifluorochloromethane based on total mols ofthis material and the 1,1,1,3,3,3-hexafluoroisopropyl trifluoroacetate.

Fluorotrichloromethane, a component of the novel azeotropic compositionof this invention, is a well-known commercially available material.

In the preferred embodiments of the invention, fluorotrichloromethane isadded to a crude reaction mixture obtained from the preparation of1,1,1,3,3,3-hexafluoroisopropyl trifluoroacetate and then the dilutedreaction mixture is fractionally distilled to obtain the azeotropiccomposition of this invention, and thus to separate the ester fromby-products, starting materials, etc. In a currently preferredembodiment fluorotrichloromethane can be employed as a diluent orreaction medium for the preparation of 1,1,1,3,3,3-hexafluoroisopropyltrifluoroacetate using any suitable process, such as directesterification or electrochemical fluorination as described above.Subsequent fractional distillation of the resulting crude reactionmixture, which includes fluorotrichloromethane, then gives the inventiveazeotrope in high degrees of purity.

Because of the general characteristic of binary azeotropes which allowsthe obtaining of the azeotropes from mixtures containing an excess ofeither of the components, the inventive azeotrope can be obtained frommixtures containing either fluorotrichloromethane or1,1,1,3,3,3-hexafluoroisopropyl trifluoroacetate in excess of the molarratio of the components of the azeotrope.

Due to the inert nature of fluorotrichloromethane, the azeotropiccomposition of this invention can be used without separation of thecomponents for further reactions involving the ester component, such asbasic hydrolysis to give 1,1,1,3,3,3-hexafluoroisopropanol and thecorresponding salt of trifluoroacetic acid. The1,1,1,3,3,3-hexafluoroisopropanol is a known solvent for nylon-typepolymers and its polymer solutions may be used for coatings, spunfibers, or self-supporting films. Also, it can be converted tohexafluoroacetone which is a known valuable chemical. The potassiumtrifluoroacetate can be treated with H₂ SO₄ to recover trifluoroaceticacid.

EXAMPLE

The following run illustrates the preparation of the azeotropiccomposition of this invention by the reaction of1,1,1,3,3,3-hexafluoroisopropanol with trifluoroacetyl fluoride in thepresence of fluorotrichloromethane as diluent and subsequentdistillation of the reaction mixture.

To a stirred 410 cc glass reactor immersed in a cold bath (-6° C to 0°C) were added 44.8 gm pyridine and 70.3 gm fluorotrichloromethane. Afterthe reactor contents cooled to 0° C, 75.5 gm1,1,1,3,3,3-hexafluoroisopropanol was added. Trifluoroacetyl fluoride(84.3 gm) was added slowly to the vapor phase in the reactor at anoverall rate of about 100 gm/hr; however, flow of trifluoroacetylfluoride into the reactor was intermittent as flow was interruptedperiodically in order to maintain the temperature of the reactionmixture between 0° and 20° C. After completion of trifluoroacetylfluoride addition (50 min.), the reaction mixture was allowed to warm to21° C over a 5-hour period. Fractional distillation of the resultingreaction mixture gave a fraction (36.4 gm) consisting of an azeotropeboiling at 22° C at 747 torr and containing 17.5 mol percent1,1,1,3,3,3-hexafluoroisopropyl trifluoroacetate and 82.5 mol percentfluorotrichloromethane, as well as other higher boiling fractionscontaining predominantly 1,1,1,3,3,3-hexafluoroisopropyltrifluoroacetate.

In order to confirm the existence of the above-described azeotrope whichwas obtained from an ester-rich mixture, the azeotrope was also obtainedby fractional distillation of a fluorotrichloromethane-rich mixtureoriginally containing 69.4 gm fluorotrichloromethane and 14.7 gm of asolution containing about 85 mol percent 1,1,1,3,3,3-hexafluoroisopropyltrifluoroacetate and about 15 mol percent fluorotrichloromethane. Theresulting azeotrope (43 gm) possessed the same boiling point andcomponent ratio as described above.

The above-described runs establish the existence, composition andboiling point of the inventive azeotrope.

Chemical shift and multiplicity data of the single proton of1,1,1,3,3,3-hexafluoroisopropyl trifluoroacetate by proton nmr analysisand fragmentation pattern of the compound by mass spectral analysis wereconsistent with the assigned structure. The structure was furtherverified by basic hydrolysis of 1,1,1,3,3,3-hexafluoroisopropyltrifluoroacetate to the known compounds1,1,1,3,3,3-hexafluoroisopropanol and potassium trifluoroacetate.

While this invention has been described in detail for the purpose ofillustration, it is not to be construed as limited thereby but isintended to cover all changes and modifications within the spirit andscope thereof.

I claim:
 1. An azeotropic composition which contains about 17.5 molpercent of 1,1,1,3,3,3-hexafluoroisopropyl trifluoroacetate and about82.5 mol percent fluorotrichloromethane, which composition boils atabout 22° C at about 747 torr.